The present invention relates to high-lift devices for aircraft wings and, more particularly, to the actuating system for moving either a trailing edge flap system or a leading edge slat system between extend and retract positions.
The aerodynamic design of modern aircraft wings is a compromise between many conflicting requirements, thus limiting their optimum aerodynamic performance to a small portion of their total flight envelope. Obviously, great emphasis must be placed on cruise configuration, as this is the regime most frequently experienced. However, contemporary wings must be configured to include high-lift devices such as flaps and slats, which are, in effect, extensions of the wing. Flaps and slats are used to enhance lift during takeoff and landing and yet may be retracted when the aircraft is in a cruise configuration.
The system which drives the mechanism which supports and provides the kinematics of translation and rotation of the high-lift device itself is governed by the same Federal Aviation regulation as to airworthiness that govern the overall high lift system. Historically, there have been two different approaches to these drive systems in large commercial airplane applications. Systems where the motion is pure rotation about a simple hinge have used hydraulic cylinders properly matched for synchronization of the segmented lift device. However, the cases where the flap requires large translation as well as rotation of the lift device torque tube drive systems have generally been employed which in turn drive various types of linear actuators located at various stations along the torque tube drive. Torque tube drives must be able to transmit full hinge moment from one wing to the other so as to avoid asymmetrical positioning of the lift device. Under the airworthiness regulations, the airplane must demonstrate safe flight with the high-lift devices asymmetrically positioned or else demonstrate by calculation that the conditions which allow asymmetry are improbable beyond a predetermined probability factor. The nature of the high-lift device is such that in the asymmetrical condition the wing with the lift device retracted stalls before the wing with the device extended. When one wing stalls, of course, it causes the airplane to roll.
All existing flap or slat torque tube drive systems used in large commercial airplanes to date locate the drive unit in the middle of the drive system and transfer power out each wing. All these aircraft must employ some device to prevent asymmetrical or uncommanded positioning of the lift device in the event of a failure of the torque tube. The protection generally consists of no-back devices at each drive station in combination with a computerized electrical asymmetry monitor for shutdown, or alternately, asymmetry brakes in combination with a computerized asymmetry and runaway protection system. The no-back device is required to prevent the air loads acting on the high lift device from driving the surface in the opposite direction. The asymmetry brakes lock the entire system when the asymmetry condition is detected by a sensing system. All these devices are susceptible to latent failures in that one of these devices can fail and will not be detectable until the second failure occurs. This necessitates periodic physical inspections of the device to examine for failures to achieve the required reliability levels.
Super critical wing geometry dictates thin shell flap structure as well as flaps which require large translation as well as rotation of the flaps. Large translations dictate the requirement for a flap driving mechanism which provides equal motion to prevent skewing, i.e. the flap drive at each hinge must be synchronized to extend and retract together.
It is an object of this invention to provide a new high-lift device drive system architecture which:
(a) has the ability to operate the high-lift device with one power source inoperative and without impacting the crew workload or operating procedures;
(b) requires two independent and separate mechanical failures before the device can go asymmetrical and one of the failures must be a broken torque tube;
(c) does not require flight crew action to detect asymmetry, and
(d) passive failure of any device is detectable from outside the wing.